More Screen Time Tracked With Faster Working Memory in Teens, 8-Year Finnish Study Finds

An eight-year follow-up of 260 Finnish adolescents found that higher self-reported screen time and lower unsupervised physical activity were linked to faster reaction times and better overall cognition scores at age 16, while activity measured by wearable sensors showed no such connection.

Eight-Year PANIC Cohort Followed Finnish Children From Age 8 to Adolescence

The findings come from the Physical Activity and Nutrition in Children (PANIC) study, an ongoing cohort based in Kuopio, Finland, that has followed a general population of children since 2006. Researchers from the University of Jyväskylä and the University of Eastern Finland recruited 736 first-graders aged six to nine, of whom 512 completed baseline testing. Attrition continued at each wave: 437 children returned for a two-year follow-up, and by the eight-year mark, when participants averaged 15.8 years old, 260 adolescents (136 boys, 124 girls) had complete data on physical activity, sedentary time, screen time, and cognition. That is about 35% of the children originally invited, a retention rate the researchers report is consistent with the demographics of those who dropped out. Cognition itself was measured only at this single follow-up point, using the CogState battery, a computerized test suite that scores reaction time, response accuracy, and working memory across several timed card tasks. The full study appears in the August 2026 issue of Pediatric Exercise Science.

More Self-Reported Screen Time Tracked With Faster Reaction Times, Not Slower

According to the study, adolescents who reported more cumulative screen time from childhood through age 16 had faster reaction times on two working-memory tasks and higher overall cognition scores, associations the authors say held up after correcting for multiple statistical comparisons. Self-reported non-screen sedentary time, meaning time spent reading, drawing, or playing board games rather than looking at a screen, showed a similar direct link to faster reaction time on one memory task but a link to poorer accuracy on another. Self-reported unsupervised physical activity, unstructured play and exercise without adult supervision, was tied to poorer accuracy on the hardest working-memory task, though the researchers note that particular result did not survive the correction for multiple testing and should be read cautiously.

The chart below only includes associations the researchers report as statistically significant after that correction. Because faster reaction time and higher accuracy both count as better performance but move in opposite numerical directions on a standard scale, each row is labeled by outcome type: "speed" rows are reaction-time measures, where a negative value means a faster, better result, while "accuracy" and "cognition" rows are scored so a positive value means a better result.

The researchers propose that non-screen sedentary and screen-based activities, including homework, reading, and structured video games, may involve cognitively engaging tasks that unstructured free time does not consistently offer. They note the pattern runs against several earlier cross-sectional studies linking organized sports and active school commuting to better adolescent cognition, and say the explanation likely depends on what specific activities each category of screen or unsupervised time actually contained, a detail their questionnaire did not capture.

Organized Sports Tracked With Boys' Memory, Light Activity With Girls'

The associations split along sex lines. Among boys, higher self-reported cumulative time in organized sports tracked with faster reaction times on a working-memory task. Boys in the cohort also reported roughly 59% more organized-sports time than girls, an average of about 33 minutes a day compared with 21, a gap calculated directly from the study's own reported means. Among girls, the relevant channel ran through device-measured light-intensity activity instead: girls with more sensor-recorded light activity, of the kind involved in walking or standing rather than sitting, showed better accuracy on the same memory task, a link the researchers did not find in boys. Formal interaction tests confirmed that difference was unlikely to be chance for both the light-activity finding (interaction p=0.025) and for a related sex split in how screen time tracked with reaction time (interaction p=0.008).

Girls in the cohort logged about 50% more non-screen sedentary time than boys, again a figure calculated from the study's own means, while boys logged more screen time and more unsupervised activity overall. The authors suggest one possible explanation: light activity among girls may often double as socializing with peers, a cognitively engaging context that differs from the more solitary or higher-intensity patterns more common among the boys in this cohort.

Wearable Sensors Found None of the Associations Self-Reports Detected

Of the 260 adolescents with complete self-reported data, only 171 also had valid readings from a combined heart-rate-and-movement sensor worn on the chest for at least four days at each exam. Across that device-measured subgroup, none of five activity categories, total activity, light activity, moderate-to-vigorous activity, vigorous activity, or sedentary time, showed a statistically significant link to any cognition measure. That stands in contrast to the five self-reported associations described above that the authors report survived correction for multiple comparisons. The researchers suggest a chest-worn sensor can register a heart-rate response without registering whether an adolescent was doing homework, playing outdoors, or scrolling a phone, context that self-report questionnaires, imperfectly, do capture through named activity categories. That gap does not settle whether the self-reported associations reflect real behavioral effects or mainly recall and reporting patterns; the authors themselves raise that possibility rather than resolving it.

The study also cannot establish which came first. Cognition was assessed only once, at the eight-year mark, so the researchers could not rule out reverse causation: that adolescents who were already sharper thinkers approached unsupervised time and screens differently, rather than screens shaping their cognition. They partly addressed this by statistically adjusting for each child's nonverbal reasoning score measured at the study's outset, before most of the tracked screen time and activity had accumulated, which reduces but does not eliminate the risk that the direction runs backward. Readers interested in how another common daily habit tracks with measurable brain outcomes in large cohorts can see a related pattern in research on ultra-processed food intake and cognitive decline, another case where a widely debated behavior shows a measurable but not fully causal link to how the brain performs.